1. Field of the Invention
The invention relates to an apparatus for driving a voice coil motor actuator.
2. Description of the Related Art
In a small camera module equipped in mobile devices, such as a cellular phone or a smart phone, an auto focus (AF) function is an essential function for definitely photographing still images or moving pictures. As an actuator for auto focus of the camera module, a voice coil motor (VCM) actuator has been widely used recently and a VCM driving integrated circuit (IC) serves to drive the VCM actuator.
The auto focus function is performed as follows. First, when a position of a lens barrel mounted with a magnet is detected by using a hall sensor and a driving signal is provided to the VCM actuator based on a detected position of the lens barrel and an input target position, a driving force is generated between a coil of the VCM actuator and a magnet mounted in the lens barrel and thus the auto focus function is performed while the position of the lens barrel moves to a focal position.
However, a magnetic force of the magnet within the VCM actuator is changed and thus driving performance of the VCM actuator may be changed, in which the magnetic force of the magnet may be changed depending on the reduction in the magnetic force of the magnet or the change in surrounding temperature and the position of the magnet attached to the lens barrel may be changed by a gravity force depending on a posture of the actuator.
Further, when a focus is searched, a searched focal distance is offset in a predetermined direction by a sensor warpage of the camera module, a tilt of the actuator, and the like and thus a focal position may be biased.
Further, when a driving signal is provided to the actuator by a PWM method at the time of driving the actuator for the auto focus, switching noise occurs and thus noise is included in the driving signal, such that noise may occur or image noise may occur.
Further, with the miniaturization of the camera module, there is a need to minimize a mounting area of the VCM actuator and the apparatus for driving an actuator.
Japanese Patent Document, JP 2013-83597 A describes a position detection apparatus and a position detection method capable of securing high linearity without relying on temperature. However, JP 2013-83597 A does not yet describe or suggest a disposition of a magnetic sensor, a driving coil, and the position detection apparatus for minimizing the mounting area of the VCM actuator and the apparatus for driving an actuator.
Therefore, a need exists for an apparatus for driving a VCM actuator capable of compensating for a deviation in a magnetic force of a magnet due to a change in surrounding temperature and a posture of the actuator, compensating for an offset depending on characteristics of an optical lens and an image sensor, a warpage of the image sensor or a tilt of the actuator, or the like, removing switching noise of an output driver, and having a minimized mounting area.